This invention relates to a structure for connecting the plates of an alkaline battery, such as a nickel-cadmium or nickel-zinc battery, to battery terminals, and to a method of connecting the plates to the terminals. The invention provides alkaline batteries which have uniform characteristics, which are stable in performance, which are high in reliability and which have excellent high-rate charge and discharge characteristics.
In general, in an alkaline battery, a plate assembly is formed by winding or laminating positive and negative plates with a separator interposed therebetween. The plates are wound in such a manner that the cores of the plates are partially protruded from the end faces of the plate assembly, and the exposed (mass-free) parts of the plate are welded to connecting pieces which are connected to the terminals (or to the container and the cover of the battery which are the negative terminal and the positive terminal).
There have been proposed a variety of methods of connecting the plates and terminals of an alkaline battery of this type. However, none of them provide alkaline batteries which exhibit optimum characteristics.
For instance, U.S. Pat. No. 3,732,124 has disclosed a connecting piece having a current collector which is made up of a flat portion and edge portions which are extended downwardly and vertically from the flat portion. The edge portions are mounted on the exposed (mass-free) part of the plate so that the edge portions vertically cross the exposed part of the plate, which theoretically allows the edge portions to be positively welded to the exposed part of the plate. However, in practice, since the edge portions are partially deformed or inclined by the pressure which is applied during the welding operation, the edge portions do not vertically cross the exposed part of the plate at all of the contact points, and accordingly the connecting piece cannot be uniformly and firmly welded to the exposed parts of the plate core. Attempts have been made to increase the strength of such welds by changing the welding conditions in various ways, however, often the current collector changes dark violet and sometimes the material becomes brittle or the current collector becomes molten.
U.S. Pat. No. 3,960,603 has disclosed a method in which a number of samll holes are cut in the current collector of a connecting piece and edges or protrusions are formed around the small holes, so that the edges or protrusions are welded to the exposed (mass-free) part of the plate. However, this method is still disadvantageous for several reasons. In practice, the welding points are not steady. As a number of edges or protrusions are employed for welding, the strength of the welds is low as a whole, and it is difficult to provide a predetermined welding strength. Accordingly, sometimes the plate assembly can be readily removed from the connecting pieces, with the result that the batteries are non-uniform in performance.
FIG. 1 shows a typical conventional connecting piece which has been disclosed by the aforementioned U.S. Pat. No. 3,732,124. FIG. 2 shows the connecting piece in FIG. 1 welded to a plate assembly. The connecting piece 1 is made of a thin nickel-plated steel plate, for example, and comprises a lead 2 connected to a terminal of the battery, and a current collector 3 which is welded to the exposed (mass-free) part of a plate. The current collector 3 includes a flat portion 7b and edges 7a extended vertically from the flat portion 7b. The edges 7a of the current collector are mounted on the exposed (mass-free) part 5 of the plate 4 in such a manner that the edges 7a cross the exposed part 5. The edges 7a are welded to the exposed part 5 of the plate with welding electrodes set on the upper surface of the current collector under pressure.
Several problems can occur in the use of a connecting piece such as that described above. First, the connecting piece edges 7a are not always vertically extended from the flat portion 7b. Secondly, even if the edges 7a are vertically extended from the flat portion 7b, the edges 7a do not always vertically cross the exposed part of the plate. For these reasons, when the pair of welding electrodes are set on both end portions of the current collector, the edges 7a are pushed by the welding electrodes thus being inclined inwardly or outwardly through slipping off on the exposed part 5 of the plate. As a result, frequently the edges 7a are not completely engaged with the exposed part 5 of the plate, and accordingly the former are incompletely welded to the latter. That is, the disclosed connecting piece is still disadvantageous in that the edges are not positively welded to the exposed part of the plate at all the welding points.
In order to eliminate this difficulty, a variety of methods have been proposed in which the edge of the exposed part of the plate is set at the same level, the plates are modified in configuration, the material of the connecting piece is changed, and the welding conditions are improved. However, none of these methods are satisfactory in practice. On the other hand, the height of each edge extended vertically from the flat portion of the current collector is generally about two to five times the thickness of the current collector so that the connecting piece can be readily formed by bending the steel plate. The above-described difficulty may be eliminated by increasing the height of each edge so that the latter is deeply engaged with the exposed part of the plate. However, in this case, it is necessary to increase the width of the exposed (mass-free) part 5 of the plate, i.e., it is necessary to decrease the effective area of the plate, and accordingly the battery operating characteristics are degraded. If the edges of the current collector are deeply engaged with the exposed part of the plate, then they may contact with the other plate of opposite polarity so that the battery will be internally short-circuited and will no longer be serviceable. Thus, none of the conventional welding methods are satisfactory in practice.